Due Date Calculator

One of the first questions every expectant parent asks is: when is the baby due? This due date calculator gives you your Estimated Due Date (EDD), current pregnancy week, and trimester — based on your last menstrual period or conception date.

How to Use This Calculator

1. Select your method: Last Menstrual Period or Conception Date.
2. Enter the relevant date.
3. Enter your average cycle length (if using LMP — default is 28 days).
4. Click Calculate to see your due date, gestational age, and key milestones.

Naegele's Rule

The standard medical formula for due date calculation:

EDD = LMP + 9 months + 7 days (for 28-day cycle)

Equivalently: EDD = LMP + 280 days

For cycles other than 28 days, add or subtract the difference (e.g., 32-day cycle: add 4 days to EDD).

Due Date Ranges

• Early term: 37 weeks 0 days to 38 weeks 6 days
• Full term: 39 weeks 0 days to 40 weeks 6 days
• Late term: 41 weeks 0 days to 41 weeks 6 days
• Post-term: 42 weeks 0 days and beyond
• Only 5% of babies arrive exactly on EDD; most arrive within 2 weeks of the date

Common Mistakes to Avoid

• Planning births too rigidly around the due date — The EDD is an estimate. Plan for a window of 37–42 weeks. Making hard commitments (travel, work) based on exact due date is risky.
• Using the wrong LMP date — Use the first day of your last menstrual period, not the last day.
• Ignoring ultrasound dating — If a first-trimester ultrasound gives a different date than LMP calculation, OBs typically adjust to the ultrasound date, especially if there's more than 1 week difference.

Frequently Asked Questions

Is a due date the same as 9 months of pregnancy?

Not quite. Pregnancy is approximately 40 weeks (10 lunar months or about 9 calendar months and 1 week) from LMP. The common "9 months" is an approximation.

Can the due date change after ultrasound?

Yes — if the ultrasound measurements differ from LMP-based dating by more than a week, your OB may adjust the EDD to match ultrasound findings.

What happens if the baby is late?

Most providers monitor closely at 41 weeks. Induction is often offered between 41 and 42 weeks depending on maternal and fetal wellbeing indicators.

When should I call my doctor after getting my due date?

Prenatal care typically begins at 8–10 weeks. The sooner you establish care, the better. First trimester visits confirm the pregnancy, date it by ultrasound, and screen for early complications.

Conclusion

Your due date is a milestone for planning, preparation, and care scheduling — but remember it's always an estimate. Use this calculator to get your EDD quickly, then confirm it with your healthcare provider at your first prenatal visit.

Related: Pregnancy Calculator | Conception Calculator | Ovulation Calculator | Pregnancy Weight Gain Calculator